1. Field of the Invention
The present invention is related to AlxGa1-xN-cladding-free nonpolar III-nitride based laser diodes (LDs) and light emitting diodes (LEDs).
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within parentheses, e.g., (Ref. X). A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
At this time, existing gallium nitride (GaN) based edge-emitting LDs are usually c-plane structures (Refs. 1-3). These devices have found applications in several consumer products. However, to achieve effective optical mode confinement in these devices, the inclusion of aluminum-containing (Al-containing) waveguide cladding layers, such as AlxGa1-xN/GaN superlattices, is required. These AlxGa1-xN/GaN superlattices present significant epitaxial growth challenges, reduce the epitaxial material quality, and increase the operating voltage of the device. Superlattice growth also poses significant problems for reactor stability and reproducibility.
Additionally, due to their orientation along the polar c-plane, these devices suffer from the quantum confined Stark effect (QCSE), which spatially separates the electron and hole wave functions and limits their radiative efficiency (Ref. 4). This results in the requirement for thin quantum wells, which are generally less than 40 angstroms (Å) in thickness, and typically have a thickness that ranges between 25-40 angstroms.
Unlike GaN-based optoelectronic devices grown on c-plane substrates, structures grown on nonpolar substrates (e.g., m-plane or a-plane) do not suffer from polarization-related electric fields, since the polar c-axis is parallel to any heterointerfaces (Ref. 5). Thus, the present invention implements thicker quantum wells using nonpolar Group-III nitride (III-nitride) structures, due to the lack of polarization fields. Moreover, these thicker quantum wells are thick enough to function as an effective optical waveguide in a laser diode, and thus no substrate with a lower index of refraction is close to the optical mode, which allows for the removal of the troublesome AlxGa1-xN/GaN superlattices that are required for optical guiding in similar devices grown on c-plane substrates.